Assessment Comments
Assessment is based on (1) information from the IDNR Wildlife Bureau, and (2) results of a fish kill investigation in March of 2007.
Basis for Assessment
SUMMARY: The Class B(LW) (aquatic life) uses are assessed (evaluated) as "partially supported” based on the results of a fish kill investigation in March 2007. Information from the IDNR Wildlife Bureau suggested that the Class B(LW) uses were assessed as "fully supported" for previous assessments. The fish consumption uses remain "not assessed" due to the lack of water quality information upon which to base an assessment.
EXPLANATION: The Class B(LW) (aquatic life) uses are assessed (evaluated) as "partially supported" based on the results of a fish kill investigation in March 2007. This kill occurred on or before March 13, 2007. The kill was attributed to “unknown” causes with natural causes suspected. About 1,000 dead bullheads and 100 minnows were found along the southeast side of the shallow lake, not far from where manure runoff was entering the lake. The fish likely died from low oxygen levels over the winter. According to DNR environmental investigators and fisheries staff, the fish kill cannot be directly attributed to runoff from the feedlot, as the fish appear to have been dead for weeks.
According to the IDNR assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2004-2007) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.” If a cause of the kill was not identified during the IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.” Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5). Waterbodies affected by such fish kills will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation.
Fish consumption uses remain "not assessed." In general, Iowa wetlands are not managed for recreational fisheries; thus, fish contaminant monitoring is not typically conducted at these waterbodies.
